1. Field of the Invention
The present invention is directed to conveyor systems, and more particularly to drive assemblies for accumulation conveyor systems.
2. Description of Related Art
Conveyors are used to transport goods and packages in all types of environments and experience especially heavy use in manufacturing and shipping industries. In addition, characteristics of the flow of goods and packages along such conveyor systems, such as timing and positioning of the goods and packages, must often be tailored to the needs of the manufacturer or shipper. Accumulator conveyor systems are divided into zones in which a driving force may be selectively applied to a conveying surface which provides each package with a stopping position. As a result, packages or goods may be accumulated in successive zones for eventual discharge from the conveyor.
As an example, U.S. Pat. No. 5,862,907 to Taylor (“Taylor”) discloses an accumulation conveyor 10 that is divided into a plurality of accumulating zones A, B, C, D and E, as shown in FIG. 1 of Taylor. The conveyor 10 includes a conveying surface, in this case a plurality of rollers 14, that are selectively driven under the control of a plurality of accumulation modules 20A-E that correspond to the accumulating zones. Each module 20 is capable of communication with its neighboring or adjacent module in the upstream and downstream directions through communications cables 42A-E. Photoelectric or ultrasonic sensors 28 are used to determine the presence or absence of an item or package within each of the accumulating zones. Thus, when a sensor fails to detect a package in a downstream zone, its module communicates with the upstream zone to activate its conveying surface and convey an object held therein to the downstream zone.
Despite improvements in the control systems of conveyors, conventional conveyors have other areas in which improvements are needed. For instance, conventional conveyor drive systems include chain drives that positively drive every roller in roll-to-roll conveyors. The drive system is centralized and a single motor drives loops of chains that run under the conveyor from zone to zone. Each chain operates a drive shaft in each zone and engagement of the drive shaft is controlled by a mechanical clutch. The drive shaft, in turn, drives other chains that are connected to each individual roller in the zone. Such chain drive systems involve the use of many moving parts which generally decreases reliability and increases maintenance needs of the conveyor system.
One type of clutch often used in the chain drive systems is a spring wrap clutch. Spring wrap clutches are high-maintenance item, particularly over extended periods of use. Also, spring wrap clutches make noise when engaging and disengaging, and a large number of clutches combined with the noise of the other parts of the chain drive system result in a noisy conveyor system that is unpleasant for workers. An alternative to the spring wrap clutch is a pneumatic clutch, but pneumatic clutches are usually expensive and require a supply of compressed air to operate. Clutches also have the problem of causing a “hard start” wherein low-slip clutches engage suddenly, and present a jarring impact to the drive system.
Therefore, it would be advantageous to have a conveyor system that is capable of zero pressure control of accumulation while at the same time having a drive system capable of relatively quiet operation and requiring low maintenance, and a reasonable cost.